It's perfectly fine to use the same tires front and rear on the B2, it's the same thing as the T2 besides the body and front shock tower. If you want to get a really large variety of on-road tires, you may want to look at getting 12mm hex adapters so that you can run 1/10th scale on-road tires:
http://thetoyz.com/cart/thetoyz_deta...cat_name=RC18T